[Paintwerks]

You need the Pace headers as the outlet faces forward. The OEM LSA headers face to the rear and will not fit in the Pace engine bay.

As an aside, we have a set of GM (HSV) cats that have been specially fabricated to fit the Pace 427 undercar system (will work with LSA, L76 and L98 motors) available to rent in order to pass the IM240 test. They feature a traditional 3 bolt style flange at the outlet side that will fit up to the pipes that pass through the chassis. We went with 2.5" piping for the rest of the system.

You can then get a set of high flow cats made to fit up if you so desire for everyday use.